Defects that are prone to occur in the welded area of submerged arc welded steel pipes include pores, hot cracks, and undercuts.
1. Bubbles. Bubbles mostly occur in the center of the weld bead. The main reason is that hydrogen is still hidden inside the welded metal in the form of bubbles. Therefore, the measure to eliminate this defect is to first remove rust, oil, moisture, and moisture from the welding wire and weld. Substances are followed by drying the flux well to remove moisture. In addition, it is also effective to increase the current, reducing the welding speed, and slow down the solidification rate of the molten metal.
2. Sulfur cracks (cracks caused by sulfur). Cracks are caused by sulfides in the sulfur segregation band entering the weld metal when welding plates with strong sulfur segregation bands (especially soft-boiling steels). The reason for this is the presence of hydrogen in iron sulfide and steel with a low melting point in the sulfur segregation zone. Therefore, to prevent this from happening, it is also effective to use semi-killed steel or killed steel with fewer sulfur-containing segregation bands. Secondly, it is necessary to clean and dry the weld surface and flux.
3. Hot cracks. In submerged arc welding, hot cracks can occur in the weld bead, especially in the arc starting and arc extinguishing craters. To eliminate such cracks, backing plates are usually installed at arc starting and arc extinguishing, and at the end of coil butt welding, the spiral welded pipe can be reversed and welded into stitch welding. Hot cracks are prone to occur when the weld stress is high, or when the weld metal is very high.
4. Involvement of welding slag. Engaging in welding slag means that a part of the welding slag remains in the weld metal.
5. Poor penetration. Insufficient overlap of internal and external weld metal, and sometimes incomplete penetration. This condition is called insufficient penetration.
6. Undercut. The undercut is the appearance of a V-shaped groove at the edge of the weld along the centerline of the weld. The undercut is produced when conditions such as welding speed, current, and voltage are not appropriate. Among them, too high a welding speed is more likely to cause undercut defects than unsuitable currents.
Post time: Nov-03-2022